INFLUENCE OF ENVIRONMENT ON SEX 229 



and the accessory male organs. Some of the controls showed partial 

 regressive changes but the majority remained perfectly normal. 



The significance of the words at head of columns in the tables is as 

 follows: 'Specimen', identification number; 'length', length of shell of 

 specimen in millimeters; 'days', number of days duration of experiment; 

 Tenis', 'Gonad', 'Seminal vesicle', condition of those organs in the 

 prepared specimens. 



Experiment 2 (Tables 3 and 4). Carried on in floating live-cars of 

 the Marine Biological Laboratory, Woods Hole. This is similar to 

 the preceding experiment except that it was performed under more 

 nearly normal concUtions. It shows the same degeneration of organs 

 in the segregated males. Here and there among the controls (table 4) 

 we find a specimen in which the activity of the testis is reduced, or 

 there is slight degeneration; this is not unexpected, since a few degenerate 

 males are found in normal colonies. 



The results of experiments 1 and 2 strengthened the suspicion 

 that the large female Crepidulas of the colonj^ exercised some 

 influence upon the small male members of the same colony. 

 The preservation of the male character seems to depend on the 

 presence of the larger animals in the same neighborhood with the 

 males. Another experiment confirmed this still further. 



Experiment 3. All the large females were removed from two colo- 

 nies leading the smaller animals which had been clustered about them 

 untouched. It was assumed, though it could not be made certain, 

 that the usual majority of males was present. The shells occupied 

 by the colonies and inhabited by the hermit crabs were replaced, after 

 removal of the females, in the aquarium and left for fifteen days. At 

 the end of that time all the smaller Crepidulas were fixed and sectioned. 

 Nine out of the eleven specimens showed that they had been func- 

 tional males, but that the testes had degenerated to various degrees. 

 The presence of the seminal vesicle with sperm in it proved that the 

 testis had recently been active, even though the testes of some indi- 

 viduals were reduced to the neuter condition. 



Two of the eleven specimens showed that they had not been males 

 when the experiment was begun; for the seminal vesicle was not 

 developed. 



MALE DEVELOPMENT IN NEUTER INDIVIDUALS 



It is possible to show, in Crepidula plana, not only that the 

 preservation of the male phase depends upon the proximity of 

 larger individuals, but that 'sexually inactive' or 'neuter' speci- 

 mens wdll rapidly develop male characteristics when brought into 



